Copyright © A. Filippone (1996-2001). All Rights Reserved.

Aerodynamic Drag

Viscous Drag


Viscous drag (or skin friction drag) is due to the stresses on the aerodynamic surfaces and in the boundary layer. The decreased momentum in the flowfield results in a corresponding loss of momentum of the aerodynamic system. Some of the physical aspects involved in the viscous drag loss are: presence of shear layers, turbulent transition, boundary layer separation.

The amount of energy losses depends largely on the aero- hydrodynamic system. On a sailing boat it can range between 1/3 and (nearly) the total drag, depending on the speed of the craft (at low speeds the viscous drag is large, in percent, whereas the wave drag is low). Some typical viscous losses are listed below:

Table 1: Summary of viscous drag
supersonic fighter 25-30 %
large tranport aircraft 40 %
executive aircraft 50 %
VTOL aircraft 70-80 %
underwater bodies 70 %
ships at low/high speed 90-30 %
gas pipelines 90 %

Reduction Methods

Methods for viscous drag reduction rely on techniques that alter the turbulence structure and/or the wall characteristics. These methods are both powered (active methods) and unpowered. Active methods widely used include

The are also the passive methods, such as vortex generators, along with appropriate design of the aerodynamic surfaces, by minimizing the wetted area and the volume. Other sophisticated techniques include:

Selected References

  • Hoerner SF. Fluid Dynamic Drag, Hoerner Fluid Dynamics, 1965.

  • AGARD. Special Course on Concepts for Drag Reduction, AGARD Report R-654, 1977.

  • AGARD. Special Course on Subsonic/Transonic Aerodynamic Intereference for Aircraft, AGARD Report R-712, 1983.

  • AGARD. Aircraft Drag Prediction and Reduction, AGARD Report R-723, 1985.

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Copyright © A. Filippone (1996-2001). All Rights Reserved.